Resinoid pocketed cutoff and grinding wheel and method of making same

ABSTRACT

A cutoff or grinding wheel having a rotatable support, preferably in the form of a disk with a thickness of up to 1 mm, formed with a multiplicity of openings along the disk periphery. Diamond particles, with or without other abrasive, are incorporated in a resinous binder and are bonded thereby in the openings of the wheel. Diamond particles have a particle size up to 40 microns and the binder is resinified by prolonged heating.

United States Patent Sekiya 51 Apr. 25, 1972 154] RESINOID POCKETED CUTOFF AND GRINDING WHEEL AND METHOD OF MAKING SAME Shinji Sekiya, 8-19 3-Chome Takanagawa, Minato-ku, Tokyo, Japan 221 Filed: May18,l970

21 App1.No.: 38,213

[72] Inventor:

[30] Foreign Application Priority Data June 14, 1969 Japan ..44/46504 [52] U.S. Cl. ..51/206 R, 51/298 [51] Int. Cl ..B24d 5/06 [58] Field of Search ..51/206 R, 206.4, 206.5, 207,

[56] References Cited UNITED STATES PATENTS 2,225,193 12/1940 Benner ..51/206.4

2,830,474 4/1958 Brauchler ..125/15 UX 3,440,773 4/1969 Hawkes ..51/206 1,507,836 9/1924 King ....51/206.4 3,048,160 8/1962 Griffin ...51/206 X 3,201,902 8/1965 Benson ..51/206 Primary Examiner-Donald G. Kelly Att0rney-Karl F. Ross 57 ABSTRACT A cutoff or grinding wheel having a rotatable support, preferably in the form of a disk with a thickness of up to 1 mm, formed with a multiplicity of openings along the disk periphery. Diamond particles, with or without other abrasive, are incorporated in a resinous binder and are bonded thereby in the openings of the wheel. Diamond particles have a particle size up to 40 microns and the binder is resinified by prolonged heating.

6 Claims, 10 Drawing Figures PATENTEDAPR 2 5 I972 SHEET 10F 3 FIG. IA

IN VENTOR. Shiry'i Sekiya Attorney PATENTEUAPR 2 5 1972 3, 6 57. 84 5 SHEET 2 BF 3 Shiljl' Sekiya IN VEN'TOR Altorne y PATENTEDAPR 25 I972 SHEET 3 OF 3 Shiry'i Sekiya INVENTOR.

Attorney RESINOID POCKETED CUTOFF AND GRINDING WHEEL AND METHOD OF MAKING SAME FIELD OF THE INVENTION The present invention relates, in general, to cutting and grinding wheels, and more particularly to wheels of the fill-in type using abrasive compositions and the method of making them.

BACKGROUND OF THE INVENTION In general, cutting wheels of the fill-in type are made by forming openings along the periphery of a metal disk, the openings serving as seats for cutting blades which are diamond particles bonded within the seats along the periphery of the disk.

It is a desirable feature of this type of cutting wheel to be able to make narrow, precision cuts, leaving a smooth finished surface.

Because of limitations in the present method of bonding the cutting blades to the wheel, it has been necessary to form cutting blades having edges which overhang the flanks of the wheel.

Since it is necessary with present cutting wheels of the fill-in type to have overhanging blades, the narrowness of the cut or kerf made by these wheels is limited.

In addition, the complexity and cost of making such wheels is increased by the shape of the blades and the size of the diamond particles used.

Another limitation associated with present wheels of this type is the inability of the resinous binders used to retain diamond particles of a size less than 40 microns. The size of the particles also causes the cut made with this type of wheel to be rough in finish and lacking in precision.

OBJECTS OF THE INVENTION It is, therefore, an object of the invention to provide a fill-in type cutting wheel capable of making extremely narrow cuts (small kerf) in a workpiece.

Another object of the invention is to provide an improved cutting wheel capable of making cuts in a workpiece which are smooth in finish.

Still another object of the invention is to provide a cutting wheel capable of making cuts of high precision.

Yet a further object of the invention is to provide a method of making a cutting wheel with the above-mentioned features which is both simple and inexpensive.

SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are obtained, in accordance with the present invention, by forming openings along the periphery of a disk having a thickness of preferably about 0.2 to 1.0 mm and a diameter preferably of 75 to 100 mm. If the disk is to be used as a grinding wheel with a broad face, it can have a thickness ofabout 80 mm and a diameter of 100 mm.

The openings can have a variety of shapes such as rectangular slots, triangles, ellipses, semicircles and diamond shapes, the slot shapes being more advantageously employed in cutting wheels rather than grinding wheels, although any of the shapes can be used for either cutting or grinding work.

In the case of a disk used as a cutting wheel and employing rectangular slots, the slots can have lengths of about 3 mm lying radially about the periphery of the wheel in a closely spaced relationship and having a width of about 1.0 mm. In addition, a second tier of slots can be formed inwardly of the periphery, at a point where the peripheral slots end.

The slots can also be formed to lie tangent to a circle having a diameter somewhat less than that of the wheel.

Although the wheel of the present invention can be composed of such standard materials as phosphor, bronze, copper, iron and steel, it is also possible, in this case, to use wheels composed of such materials as ceramic, plastic, melamine,

bakelite and polyester, thereby making it easier and less expensive to manufacture the wheels with the openings necessary for carrying the abrasive composition.

The abrasive composition, used as a cutting medium in these wheels, comprises a mixture of diamond particles having a size of 8 to 20 microns in a resinous binder, the particles comprising up to 50 percent by weight of the mixture. In any case at least 50 percent by weight of the mixture must be constituted by the binder.

Although diamond particles can be used as the sole abrasive ingredient in the mixture, it has been found advantageous, when cutting certain materials, to add other abrasive particles to the mixture, such as carbon powder, corundum, emery, garnet, silica and alundum.

The abrasive particles are added to a liquid-state phenolic resin, where they are thoroughly mixed, while powder-state phenolic resin is slowly added, along with hardening agents, to the mixture, until the mixture thickens and becomes moldable.

There are several different methods which can be employed according to the invention to complete the manufacture of the cutting wheel, such as rolling the moldable mixture into a thin sheet on the order of about 0.1 mm, or the exact thickness of the wheel, curing and resinifying the sheet at a temperature of about 40 to C. for 24 hours, forming the desired blade shape from the finished sheet by cutting or punching and coating the edges with cement for bonding within the wheel openings, flush with the flanks of the wheel or, the desired blade shapes can be formed prior to curing and resinification, then proceeding as described earlier.

Another method employed is to form the blades from the moldable sheet, partially cure them, place them in the wheel openings and continue baking to complete the curing, resinification and bonding.

Still another method in accordance with the invention is to fill the moldable mixture into the wheel openings, doctoring the mixture until it is properly shaped and flush with the flanks of the wheel and then baking to complete curing, resinification and bonding.

Since the cutting blades formed by the abrasive composition lie flush with the flanks of the wheel, it will be apparent that the width of the cut or kerf made by such a wheel is determined only by the thickness of the wheel, allowing extremely narrow cuts of great precision to be made with ease.

I have discovered, moreover, that, while a number of synthetic resins are suitable binders for the wheel of the present invention, it is important to produce by thermal transformation of the binder, a resinification" which appears to have a significant effect upon the ability of the wheel to retain the abrasive particles and permit the wheel to be used for high-pressure applications.

It is essential to the invention, however, that the resinification be applied to a composition received within the pockets of the abrasive or cutoff wheel. More specifically, it has been found that the synthetic-resin binders mentioned above form solids, semisolids and pseudoor quasi-solids by intricate polymerization among the molecules during the cooling process, but that simple curing does not suffice to retain diamond particles of a particle size of less than 40 microns with sufficient tenacity as to permit the composition to be used under high pressures in the cutting of workpieces or the like. Furthermore, the solidification or curing of the product appears to create a brittle matrix in which the particles are received, this matrix being fragmented, disintegrated or abraded in use to loosen the bond and release the particles which, consequently, are not available for cutting of the workpiece.

It has now been found, especially with a particular type of resin described in greater detail hereinafter, that it is possible to transform the binder by a process referred to herein as resinification" to overcome the disadvantages of ordinary curing of the aforementioned resins found suitable for use with diamond binders. It has been found that prolonged heat treatments at temperatures above ambient, i.e. for 12 hours or more at temperatures above 100 C., give rise to a physical transformation of the synthetic resin which transforms the binder into a tough, resilient, wear-resistant and tenacious matrix from which the diamond particles are not readily released even under the high pressures created during cutting operations. While applicant does not wish to be bound to any theory in this regard, it appears that the crystalline organization of the molecules of the binder resulting from ordinary cooling is transformed into some allotropic configuration which embraces the diamond particles more securely and is less sensitive to mechanical stress although the resinified mass may be less rigid. Applicant also does not wish to exclude the possibility that some interfacial reaction occurs between the resinified binder and diamond particles, it being noted that the retention of a diamond particle is more pronounced than the retention of abrasive particles of other composition.

The preferred binder of the instant invention is one which has been found to give remarkable results when used with diamond particles in the 8 to 20 micron particle-size range, in pocketed cutoff wheels with a maximum thickness of 1 mm, and is a phenol-formaldehyde resin of the thermosetting type. The binder may consist of phenol-formaldehyde resins of liquid or resol (stage A) type and approximately an equal amount of fully cured or partially cured stage C phenol-formaldehyde resin powder preferably of the novolac type. The cure is effected at temperatures of up to 180 C. for a period of up to 24 hours.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawing, in which:

SPECIFIC DESCRIPTION 7 In FIG. 1, there is shown a cutting wheel 1, having parallel flanks 2 and a cutting edge 2 rotatable about a central axle 3. The wheel 1 is provided with openings in the form of slots 4 distributed along the cutting edge 2 and lying along radii of wheel 1. The slots 4 are filled with an abrasive composition 5 which forms a cutting blade bonded by a cement layer 6 within the slots 4 and flush with the flanks 2 and edge 2' ofwheel 1.

In the enlarged view of one of the slots 4, shown in FIG. 2, the abrasive composition 5 can be seen to be a mixture of particles 7 in a resinous binder 8.

In FIG. 1A, there is shown an edge view of the wheel I, having a thickness T. The wheel 1 is brought to bear against a workpiece W, making a cut having a kerf W in the workpiece W, equal substantially to the thickness T ofthe wheel 1.

The wheel 10 shown in FIG. 3 is similar to that of FIG. 1 except for the slots 40 which lie tangent to a circle 9 located inwardly of the periphery of wheel 10, the slots 40 also being filled with abrasive composition 5.

The wheel 100, shown in FIG. 4, has a first tier 4a of slots 4 filled with abrasive composition 5, similar to that shown in FIG. 1. A second tier 4b of abrasive filled slots 4' lies inwardly of tier 4a, the slots 4' lying radially offset with respect to slots 4, the bottom ends 4" of slots 4 and the top ends 4" of slots 4 lying along a common line 4a.

In operation, the edge 2' of wheel 1 is brought to bear against a workpiece and rotated about axle 3, the material of wheel 1 being worn away and exposing the abrasive 5, which cuts a slot in the workpiece no wider than the wheel 1.

In the case of the wheel shown in FIG. 4, after the first tier 4a of abrasive filled slots 4 are worn away, the second tier 4b of slots 4 is exposed and brought into contact with the workpiece, thereby providing a wheel with an extended operational life.

In FIG. 5 we show a grinding wheel 11 having a cylindrical body 11' with V-shped grooves 14 formed in the peripheral surface 11', the wheel 11 being rotatable about a centrally disposed axle 13. The grooves 14 are filled with the abrasive compound 5 which is bonded therein as described previously with reference to FIG. 1.

The embodiments shown in FIGS. 6 through 9 are similar to that of FIG. 5, in they they all have cylindrical bodies 111', 211', 311', 411 respectively. The grinding wheel 111 shown in FIG. 6 is provided with semi-circular grooves 114, formed in the surface 111" of body 111, the base diameter of the semi-circle lying tangent to the curved surface 11 1".

The grooves 114 are filled with the abrasive composition 5, which is doctored to conform to the curved surface 111".

The wheel 211 shown in FIG. 7 has openings 214 extending between the flanks of body 211 and parallel with the surface 211", the openings 214 having an elliptical cross-section, with the major axis 214 lying along radii of the wheel 211, the elliptical openings 214 being tangent to, and breaking the surface of, the periphery 211".

The wheel 311 shown in FIG. 8 has openings 314 extending between the flanks of body 311' and parallel with the surface 1 1", the openings 314 having a triangular cross-section, with the bi-sectors 314' lying along radii of the wheel 311, the triangular openings 314 breaking the surface 311" along the apex 314".

In FIG. 9, the wheel 411 has a cylindrical body 411' in which diamond-shaped openings 414 extend from flank to flank through the body 411 and parallel with the surface 411", the bisectors 414 of diamond-shaped openings 414, lying along radii of wheel 411 and the apexes 414" breaking surface 411".

SPECIFIC EXAMPLES EXAMPLE I In this embodiment, 1.0 gram of diamond particles, having a size of 8 to 20 microns, was fully wetted in a mortar by 0.5 grams of resol type liquid-state phenol resin to which was added 0.5 grams of novolac type powder-state phenol resin, 0.1 grams of zinc flowers and 0.01 grams of brass powder, the ingredients being thoroughly mixed until a uniform, moldable state was achieved. Using conventional equipment, the moldable mixture was rolled into a thin sheet of 0.1 mm thickness and then cured and resinified by baking for 24 hours at a temperature of 40 to C.

In a phosphor bronze wheel, having a thickness of 0.2 mm and a diameter of 75 mm, notches, such as those shown in FIG. 1, where formed along the periphery of the wheel at 1.0 mm intervals, using conventional methods, the notches having a width of 0.1 mm and a length of 3.0 mm.

From the 0.1 mm thick hardened sheet of abrasives, pieces were cut having a width of 0.2 mm and a length of 3.0 mm, the two 0.2 mm by 3.0 mm faces being coated with an epoxy resin cement, the cut pieces then being inserted into the wheel notches and bonded in place.

The abrasive wheel thus produced was able to cut ultra-hard tungusten alloy, leaving a smooth, finished, narrow cut. Alumina plates can be cutoff similarly.

EXAMPLE II In this embodiment, the size, quantity and method of mixing the ingredients of the abrasive composition and the structure of the phosphor bronz wheel, are identical to that described in Example I, the only difference being that the pieces to be inserted in the notches are formed from the rolled sheet prior to baking, the pieces thus formed being baked individually.

EXAMPLE III In this embodiment, the size, quantity and method of mixing the ingredients of the abrasive composition, are identical to that described in Example I, the 0.1 mm thick rolled sheet being cut into pieces 1.0 mm wide and 3.0 mm long, the cut pieces allowed to cure in air and then placed in notches 0.1 mm thick and 3.0 mm long formed at 1.5 mm intervals along the periphery of a steel wheel 1.0 mm thick and 100 mm in diameter; the wheel with its filled notches was then baked at 40 to l80 C. for 24 hours, bonding and resinifying the abrasive pieces within the notches.

EXAMPLE IV In this embodiment, 1 gram of diamond particles, having a size of 8 to 20 microns, was mixed in a mortar with 1 gram of green carbon-alundum particles having a size of microns, and then fully wetted with 0.8 grams of liquid-state phenol resin, to which was added 0.4 grams of epoxy degenerated phenolic resin, 0.4 grams of novolac-type phenoic resin powder, 0.01 grams of carbon powder, 0.08 grams of zinc flowers and 0.01 grams of brass powder, the ingredients being thoroughly mixed until a uniform, moldable state is achieved.

The moldable mixture was then filled into triangular grooves, 2 mm wide and 3 mm deep, formed at 2 mm intervals along the peripheral surface of a brass cylindar, 80 mm thick and 100 mm in diameter, the moldable mixture being doctored to conform to the curved periphery of the wheel and then baked for 24 hours at a temperature of 40 to 180 C. completing the the resinification and bonding ofthe mixture.

This cylinder-shaped wheel was found to perform excellently as a grinding wheel for ultra-hard materials.

lclaim:

l. A method of making an abrasive wheel comprising the steps of a. forming a metal support rotatable about a central axis;

b. providing in said support a plurality of openings distributed about said central axis;

c. filling said openings with a composition up to 50 percent by weight of abrasive particles including diamond particles of a particle size of 8 to 20 p. in a thermosetting phenolic resinous binder, said composition being formed by mixing said adhesive particles with a portion of said binder in a liquid state and then combining therewith another portion of said binder in a solid state; and

d. bonding said composition within said openings and flush with the flanks of said support by heating same for a period and at a temperature sufficient to set and resinify said binder.

2. An abrasive cutting wheel comprising a metal diskshaped support having a thickness of up to 1 mm rotatable about a central axis, a plurality of generally radially oriented slots formed in the periphery of said support at spaced locations therealong, said slots having a width of about 0.1 to 0.2 mm and a length of about 3 mm, a resinoid composition completely filling said slots and flush with the flanks of said support, said composition consisting of at least 50 percent by weight of a resinoid binder of substantially equal parts by weight of a type-A liquid phenol-formaldehyde resin and a novolac powder phenol-formaldehyde resin cured to resinification, and an abrasive powder consisting at least in part of diamond particles with a particle size of substantially 8 to'20 microns distributed in said binder.

3. A method as defined in claim 1 wherein said support is composed of a material selected from the group consisting of phosphor, bronze, copper, iron and steel.

4. A method as defined in claim 3 wherein said diamond particles comprise about 50 percent by weight of said composition.

5. A method as defined in claim 4 wherein said composition further comprises additional abrasive particles selected from the group consisting of carbon powder, corundum, emery,

garnet, silica and alumdum.

. An abrasive wheel as defined in claim 2 wherein said support is composed of a material selected from the group consisting of phosphor bronze, copper, iron and steel. 

2. An abrasive cutting wheel comprising a metal disk-shaped support having a thickness of up to 1 mm rotatable about a central axis, a plurality of generally radially oriented slots formed in the periphery of said support at spaced locations therealong, said slots having a width of about 0.1 to 0.2 mm and a length of about 3 mm, a resinoid composition completely filling said slots and fLush with the flanks of said support, said composition consisting of at least 50 percent by weight of a resinoid binder of substantially equal parts by weight of a type-A liquid phenol-formaldehyde resin and a novolac powder phenol-formaldehyde resin cured to resinification, and an abrasive powder consisting at least in part of diamond particles with a particle size of substantially 8 to 20 microns distributed in said binder.
 3. A method as defined in claim 1 wherein said support is composed of a material selected from the group consisting of phosphor, bronze, copper, iron and steel.
 4. A method as defined in claim 3 wherein said diamond particles comprise about 50 percent by weight of said composition.
 5. A method as defined in claim 4 wherein said composition further comprises additional abrasive particles selected from the group consisting of carbon powder, corundum, emery, garnet, silica and alumdum.
 6. An abrasive wheel as defined in claim 2 wherein said support is composed of a material selected from the group consisting of phosphor bronze, copper, iron and steel. 